What is the maximum or minimum tire width I can fit on my bicycle
We often get questions on bicycles.stackexchange about fitting wider or narrower tires to bicycles. We have a large number of these with answers suiting the specific bike or style of bicycle in question, but I have been unable to find one that provides a generic answer covering off all things that need to be considered. For most bicycles, the answer is the same regardless of the specific style and sizes of tires in question.
This is intended as a canonical question that we can point closed questions to.
Maximum tire width is dependent on two main factors, clearance at the frame/fork, and the width of the rim.
As for the frame clearance this can usually be visually inspected and easily distinguished if a larger tire than the present tire will cause issues. Brakes such as V-brakes or cantilevers may also cause clearance problems with some tires so attention should be paid to them as well.
Mud or other debris should also be considered for mountain bikes and applications with fenders/mudguards. You should not run clearances so tight that one little pebble caught in the tread will hit the frame, fenders or other parts.
Think of the difference between both sizes you are considering and then split that number in half, that is the distance you will need to be able to clear on either side of the tire at the chainstay essentially. So if there is a 4 mm difference in road tires, the new size will roughly add an additional 2mm onto either side of the existing tire is one way to think about it, but the top of the tire needs to also be checked as the new tire may also be taller in addition to the increased width.
Knobs on MTB tires can also vary greatly and play a part in your decisions and fitment as well. One 2.25" tire may come out to be shorter than another more aggressive 2.25" tire due to the shape and size of the knobs.
As for rim to tire interface there are multiple guidance charts available online that give a rough estimate if a tire is compatible with a certain rim width, such as this one from J&B Importer's, a bicycle parts distributor's catalog.
As an example you can see that a rim width of 19mm (top row) should be compatible with tire width of 28mm/1.10" through 62mm or about 2.5". But seeing as 28mm is the lower end of that column somewhere in the 2.2/2.35 range would be a safer bet.
However just because it will fit on the rim does not mean it will not rub on the frame so that is what is most important.
For small changes such as from 26 x 1.95 to 26 x 2.125, or 700C x 23 to 700C x 25 you are almost certainly safe from a rim standpoint if the bicycle was factory equipped with 1.95"/700x23 tires.
To be certain, the model of rim should be referenced and the width noted.
Please also note that the same applies to going to a smaller tire size, too small of a tire on the same rim could not seal well and potentially cause flats or blowouts when the tire bead cannot seal against the rim well enough.
+1 - a nice answer. At the end of the third para I'd change to "frame, fenders, or other parts" after my own experience. You might mention different knobblies coming up different heights (or even widths if you look at the shoulders). And a typo in the last para "aslo"
Maybe mention the word "mudguards" as well as "fenders" (assuming that's what is meant by "fender") for people outside the US?
@ChrisH it was my understanding that it was generally considered bad practice to combine knobby tires and fenders. The knobs are more likely to pick up debris that can the jam in the fender leading to a crash.
@Rider_X yes, but we still have knobblies vs frame, fork, or in my case front derailleur to consider. Your comment indicates that my suggestion spoils the flow from the previous sentence
@NateW, may I add this link from Jan Heine that suggests an absolute minimum of 3mm between the tire and the closest part of the frame?